Technical Field
The present disclosure relates to a reception and transmission circuit for a capacitive micromachined ultrasonic transducer (CMUT).
Description of the Related Art
As is known, in the last few years, thanks to the developments in the field of micromachining of semiconductor materials, in particular silicon, the use of probes provided with arrays of micromachined ultrasonic transducers of a capacitive type (CMUTs) or piezoelectric type (PMUTs) has expanded.
The above transducers have extremely low consumption levels and enable, given the small dimensions, detection probes for 2D or 3D imaging to be obtained that are extremely compact and may, for example, be used in applications of medical diagnostics (in medical ultrasonographic scanners or ultrasonic tomography scanners), for example coupled to probes for intravascular diagnostics, affording important advantages in terms of portability and flexibility of use to be achieved.
Of course, there may be a wide range of further uses, even in the non-clinical field, for example for monitoring the conditions of integrity or manufacturing quality of mechanical elements to be tested or monitored.
The use of an array, constituted by an orderly arrangement, whether unidimensional, two-dimensional, or three-dimensional, of a plurality of ultrasonic transducers, facilitates processing of the signals acquired for the corresponding imaging operations.
The use of CMUT transducers may have certain advantages over the use of piezoelectric transducers, amongst which the possibility of full integration with the corresponding transmission and reception circuit.
The individual CMUT transducers may in fact be obtained in an integrated manner in one or more dice of semiconductor material, and include a membrane that faces a substrate and is able to undergo bending, during the transmitting phase, as a function of an excitation signal applied by a transmission circuit, thus generating acoustic waves that are transmitted in the surrounding environment; or, during the receiving phase, as a function of detected acoustic waves, thus generating a variation of the resulting capacitance, which may be read by a reading circuit.
The die integrating the CMUT transducer may then be coupled, for example using the flip-chip technique, to at least one further die integrating the transmission and reception circuit (including a plurality of transceiver channels, one for each CMUT), within a single package, which is compact and occupies a small space.
The integration of the transmission and reception circuits may, for example, be obtained, in an economically advantageous manner, with BCD SOI techniques, facilitating reduction of the associated power consumption.
As an alternative, each transmission circuit, and a corresponding distinct reception circuit, may be integrated in respective dice of semiconductor material, for example for separately optimizing the performance and the manufacturing techniques of the two circuits. In any case, advantageously, both dice may be housed in a same package.
In greater detail, two main techniques are known for driving a CMUT transducer, and thus for designing the associated transceiver circuit, according to whether the transducer is provided with a single electrode that is individually accessible (from the outside of the corresponding die) or with both electrodes that are individually accessible (once again, from the outside of the corresponding die).
In the former case, in a corresponding array of transducers, the bottom electrodes of the CMUT transducers are connected together, at the bottom (non-accessible underside of the die), whereas for each CMUT transducer the top electrode is available at the front (accessible upper side of the die). In the latter case, both of the electrodes are available individually for each transducer on the front of the die, at the cost, however, of a complication in the manufacturing of the same transducers and of the corresponding electrical interconnections.